// SPDX-License-Identifier: BUSL-1.1
pragma solidity 0.8.24;

import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import {ERC20Permit} from "@openzeppelin/contracts/token/ERC20/extensions/ERC20Permit.sol";

/// @title USDR — Rain Dollar
/// @notice Single fungible, basket-backed stablecoin (White Paper v3.2 §3).
/// @dev No transfer fee, no hooks, no admin-mint. Minters (PSM, CDPVault) are set
///      once at deployment and then finalized FOREVER. There is no owner, no upgrade
///      path, and no code path that can extend the minter set after finalization
///      (WP §10: "No admin-mint ... nor can a key thief").
contract USDR is ERC20Permit {
    // ---------------------------------------------------------------------
    // Errors
    // ---------------------------------------------------------------------
    error NotMinter();
    error NotDeployer();
    error AlreadyFinalized();
    error ZeroAddress();

    // ---------------------------------------------------------------------
    // Storage
    // ---------------------------------------------------------------------
    address public immutable deployer;
    bool public mintersFinalized;
    mapping(address => bool) public isMinter;

    event MinterAdded(address indexed minter);
    event MintersFinalized();

    constructor() ERC20("Rain Dollar", "USDR") ERC20Permit("Rain Dollar") {
        deployer = msg.sender;
    }

    /// @notice Add a minter (PSM / CDPVault). Only before finalization.
    function addMinter(address minter) external {
        if (msg.sender != deployer) revert NotDeployer();
        if (mintersFinalized) revert AlreadyFinalized();
        if (minter == address(0)) revert ZeroAddress();
        isMinter[minter] = true;
        emit MinterAdded(minter);
    }

    /// @notice Permanently lock the minter set. Irreversible.
    function finalizeMinters() external {
        if (msg.sender != deployer) revert NotDeployer();
        if (mintersFinalized) revert AlreadyFinalized();
        mintersFinalized = true;
        emit MintersFinalized();
    }

    function mint(address to, uint256 amount) external {
        if (!isMinter[msg.sender]) revert NotMinter();
        _mint(to, amount);
    }

    function burn(address from, uint256 amount) external {
        if (!isMinter[msg.sender]) revert NotMinter();
        _burn(from, amount);
    }
}